Re: Aggregate FILTER option is broken in v10

I wrote:
> I think possibly the best answer is to revert 8ed3f11bb.  We could
> think about some compromise solution like merging the projections
> only for aggregates without FILTER.  But that would require two
> code paths through the relevant functions in nodeAgg.c, which would
> be a substantial maintenance burden; and the extra branches required
> means that this would be a net negative for performance in the
> simplest case with only one aggregate.

Hmm ... on closer inspection, the only performance-critical place
where this matters is advance_aggregates, and that already has a check
for whether the particular aggregate has a filter.  So we could do
something like

        /* Skip anything FILTERed out */
        if (filter)
        {
            // existing code to eval/check filter expr
+
+           /* Now it's safe to evaluate this agg's arguments */
+           slot = ExecProject(pertrans->argproj);
        }
+       else
+           slot = aggstate->evalslot;

which seems like a pretty minimal extra cost for the normal case
with no filter.

Let me see what I can make of that ...

			regards, tom lane